1. Field of the Invention
The present invention relates to an image reading apparatus which is capable of reading a fingerprint and the like.
2. Description of the Related Art
As the development of a networked society, the integration of portable equipments and a radio network has been progressed, and the necessity of a security function such as personal identification has also been increased in portable equipments, which need to be downsized. As personal identification, identification by living body information such as a fingerprint has received attention, because a portable equipment which adopts this identification cannot be easily abused by another person, and living body information can never be lost unlike a key and an IC card. As a method of reading a fingerprint, a method using an optical system such as a prism is dominating.
FIGS. 9A, 9B are views showing a fingerprint reading apparatus which uses a prism. In FIG. 9A, among a top face 1a and side faces 1b, 1c of a prism 1, a finger is rested on the top face 1a and irradiated with light via the side face 1b, and light reflected on the top face 1a and coming out through the side face 1c is picked up by a CCD (charge-coupled device) camera 2. In FIG. 9B, the CCD camera 2, which is positioned on the side of a light source, picks up light scattered on the top face 1a and coming out through the side face 1b. 
Further, Japanese Unexamined Patent Publication JP-A 9-186312 (1997) discloses a liquid crystal display device in which a photoreceptor device is imbedded. This device has a condenser lens for condensing light onto the photoreceptor device, thereby imaging a face of a person who is away from a display screen.
Since the fingerprint reading apparatus shown by FIGS. 9A, 9B uses a prism, it is impossible to decrease the thickness of the apparatus and difficult to downsize the apparatus, and since the liquid crystal display device disclosed in JP-A 9-186312 has a condenser lens, it is also difficult to downsize the device.
An object of the invention is to provide a small-size image reading apparatus which shows an excellent accuracy in image reading, by a different means from the prior arts.
The invention provides an image reading apparatus comprising:
a panel including a pair of light-transmitting substrates and a plurality of photoreceptor devices which are two-dimensionally arranged and interposed between the pair of substrates, an edge of one of the pair of light-transmitting substrates being provided with a slope; and
a light source opposed to the slope of the light-transmitting substrate,
wherein an object in contact with a surface of the panel is irradiated with light transmitted within the panel, and the light returned from the object is received by the photoreceptor devices, whereby an image of the object is read.
According to the invention, light from the light source is let in through the slope of the light-transmitting substrate, and the light is transmitted by reflection on the surface of the panel, whereby a direction in which the light is transmitted within the panel can be restricted.
In other words, light from the light source enters through the slope opposed to the light source, so that light from a direction of reaching the slope at a relatively small incident angle enters in the light-transmitting substrate, whereas light from a direction of reaching the slope at a relatively large incident angle is reflected by the slope and does not enter in the light-transmitting substrate. As a result, a direction in which light travels in the panel can be restricted. Moreover, among light beams reaching the surface of the panel, a light beam reaching at an angle equal to or more than a critical angle is totally reflected. On the other hand, as for light beams reaching at an angle less than the critical angle, some of the light beams are reflected and travel in the panel again, whereas the rest go out of the panel. By reflected on the surface of the panel again and again, the light beams travelling in a direction of reaching at an incident angle less than the critical angle are screened out. As a result, a direction in which light travels in the panel can be restricted still more.
Thus, an image of an object in contact with the surface of the panel is read by using light travelling in a restricted specific direction, so that the accuracy in image reading can be increased. Moreover, since a direction in which light travels can be restricted only by forming a slope at an edge of the light-transmitting substrate and opposing a light source to the slope, another optical system such as a condenser or a spectroscope is not needed, and a downsized apparatus can be produced.
Further, the invention provides an image reading apparatus comprising:
a panel including a pair of light transmitting substrates, a plurality of photoreceptor devices which are two-dimensionally arranged and a liquid crystal layer having a variable transmittance, the plurality of photoreceptor devices and the liquid crystal layer constituting photoreceptive pixels and being interposed between the pair of substrates, an edge of one of the pair of light-transmitting substrates being provided with a slope; and
a light source for launching light into the panel,
wherein an object in contact with a surface of the panel is irradiated with light transmitted within the panel, and the light returned from the object is received by the photoreceptor devices, whereby an image of the object is read.
According to the invention, a direction in which light travels within the panel can be restricted in the same manner as mentioned before, so that the accuracy in image reading can be increased. Moreover, the panel is provided with a liquid crystal layer, and thereby a transmittance can be changed for each photoreceptive, so that a direction in which light travels within the panel can be restricted still more, and the accuracy in image reading can be increased. In addition, by controlling a transmittance of the liquid crystal layer for each photoreceptive pixel, it is also possible to use the panel for display.
Still further, the image reading apparatus of the invention further comprises liquid crystal controlling means for carrying out control of allowing light to pass through a portion of the liquid crystal layer, the portion of the liquid crystal layer being located on an optical path extending from the slope of the light-transmitting substrate to a photoreceptor device.
According to the invention, light travelling in a direction restricted in a manner as described before passes through a restricted optical path and reaches a photoreceptor device. Since a portion of the liquid crystal layer which is located on the optical path leading to the photoreceptor device is controlled so that light passes therethrough, light which passes through another path would not be received, the occurrence of noise can be prevented, and the accuracy in image reading can be increased still more.
Still further, the image reading apparatus of the invention further comprises data extracting means for extracting photoreceptive data of a photoreceptor device located on an optical path which extends from the slope of the light-transmitting substrate and passes through a portion of the liquid crystal layer through which light has passed, from among photoreceptive data of all the photoreceptor devices.
According to the invention, light which has passed through a portion of the liquid crystal layer travels through a restricted optical path and reaches a photoreceptor device. In the invention, firstly, photoreceptive data are derived from all the photoreceptor devices including a specific photoreceptor device located on the restricted optical path. Since photoreceptive data of the specific photoreceptor device associated with the portion of the liquid crystal layer through which light has passed is extracted from among all the photoreceptive data, photoreceptive data on light which has passed in another path would not be used, the occurrence of a noise can be prevented, and the accuracy in image reading can be increased still more.
Still further, in the invention it is preferable that the panel is provided with a mask for blocking light which enters via a surface of the light-transmitting substrate and reaches a photoreceptor device.
According to the invention, the panel is provided with a mask for blocking light which enters via the surface of the panel and reaches a photoreceptor device. For example, by forming the mask immediately above a photoreceptor device, light which enters via the surface of the panel can be blocked, the occurrence of noise due to ambient light can be prevented, and the accuracy in image reading can be increased still more.
Still further, the image reading apparatus of the invention further comprises photoreceptive control means for controlling the photoreceptor devices in either a totally driving mode or a partially driving mode, in the totally driving mode all the photoreceptor devices are driven, in the partially driving mode only a part of the photoreceptor devices in a certain area elements are driven.
According to the invention, it is possible to drive all the photoreceptor devices in the totally driving mode, and it is possible to drive only the part of the photoreceptor devices in a certain area in the partially driving mode. In some cases, for example, in the case of reading a fingerprint, it is not necessary to drive the photoreceptor devices in all the areas of the panel. In such a case, the photoreceptor devices are driven in the partially driving mode, whereby photoreceptor devices unrelated to image reading are not driven, and power consumption can be reduced.
Still further, the image reading apparatus of the invention further comprises liquid crystal controlling means for carrying out control of light transmittance of a portion of the liquid crystal layer to display an area of photoreceptive pixels containing photoreceptor devices driven in the partially driving mode.
According to the invention, since an area of photoreceptor devices driven in the partially driving mode is displayed, and thereby an area on which an object to be read such as a finger of the operator is put can be definitely displayed. Not only the operation is simplified, but also performance of image reading is ensured.
Still further, in the invention it is preferable that the panel is provided with a filter for transmitting, for each photoreceptive pixel, light of one wavelength band of a plurality of different wavelength bands,
the apparatus further comprises liquid crystal controlling means for controlling transmittance of the liquid crystal layer, and photoreceptive control means for controlling driving of the photoreceptor devices,
an image of each wavelength band is read by sequentially driving a portion of the liquid crystal display layer and a photoreceptor device which are contained in a photoreceptive pixel associated with each wavelength band.
According to the invention, the panel is provided with filters, each of which one of the visible light beams of red, green and blue colors passes through, for example. At first, as for a photoreceptive pixel provided with a filter for transmitting a light beam of red color, liquid crystal control of driving the liquid crystal layer and photoreceptive control of driving the photoreceptor device are carried out, whereby an image of red color is read. Next, in the same manner, an image of green color is read, and then an image of blue color is read.
Thus, portions of the liquid crystal layer and photoreceptor devices contained in photoreceptive pixels associated with the respective wavelength bands are sequentially driven, whereby without driving unrelated portions of the liquid crystal layer and photoreceptor devices, images of the respective wavelength bands can be read with a relatively small power. Moreover, since read images of the respective wavelength bands are sometimes different in resolution, the reliability of data verification can be increased by conducting data verification using all the images. In specific, this is effective for fingerprint identification or the like.
Still further, the image reading apparatus of the invention further comprises calculating means for dividing a photoreceptive level during on-conditions of the light source, by a photoreceptive level during off-conditions of the light source.
According to the invention, a photoreceptive level during on-conditions of the light source and a photoreceptive level during off-conditions of the light source are outputted, and the former is divided by the latter. Since the former is a photoreceptive level including noise and the latter is a photoreceptive level representing noise caused by ambient light unrelated to the light source, the noise can be removed in the calculation as shown above, and the accuracy in image reading can be increased still more.
Still further, in the invention it is preferable that the light source emits light of a predetermined wavelength band, and the photoreceptor devices receive light of the same wavelength band as the light from the light source.
According to the invention, by associating the photoreceptive sensitivity of the photoreceptor devices with the wavelength band of the light from the light source, for example, by using photoreceptor devices which show an excellent photoreceptive sensitivity in the wavelength band of the light from the light source, light other than the light from the light source is hard to be received, and the accuracy in image reading can be increased still more.
Still further, in the invention it is preferable that on a surface of the panel, a touch sensor or a temperature sensor is placed.
According to the invention, a touch sensor or a temperature sensor is placed on the surface of the panel, whereby the operator can conduct various kinds of input operations by operating the panel, and an operability can be enhanced. In a case where a touch sensor is used, the operator can input by pushing the surface of the panel with an input pen or a finger of the operator. In a case where a temperature sensor is used, the operator can input by moving the operator""s finger or the like close to the surface of the panel, in which case it is not necessary to touch the panel with the finger. Moreover, these input operations can be associated with various kinds of controls, and the light source can be controlled by an input operation with a finger of the operator, for example.
Still further, the image reading apparatus of the invention further comprises light source controlling means for driving the light source when it is detected that the photoreceptor devices stop receiving light.
According to the invention, the light source is driven when the photoreceptor devices detect blockage of ambient light, so that it is not necessary to give directions to start driving the light source and start reading an image, an image can be read by automatic driving of the light source, and an operability can be enhanced.